Chemistry Notes Chap3

                                     Important Questions 

Q1 Borate glazes are preferred over the silicate glazes.

Ans: The borate glazes are preferred over the silicate glazes because the borate glasses are more fusible and possess higher cofficient of enpansion than the borate glass.

Q2 What is vitreous sillica ?  Give two uses.

Ans: When the crystline sillica is heated at suffciently high temrature it melts to give the visous liquid having randon sutructure which on cooling does not readily crystllize and become rigid without having undergone the orientation into regular crystal pattern is is called viterous sillica.

Q3 Four uses of  Sodium Sillicate.

Ans:  It is used as filler for soap in soap industry
         It is use in textile as fire proof
         It is used as furniture polish
         It is used in colico printing
 
Q4 Give reaction of Al with nitric acid.

Ans:  Aluminium does not react with any concentration of NHO3, probably beacause of formation of protective layer of aluminium oxide. The acid is said to render the alluminium passive that is why the nitric acid is transported in the aluminium container.

Q5 Give equation of reaction of Al with conc. H2SO4 and NaOH.  

Ans: Aluminum is amphoteric is nature as it dissolves in both acids and base with liberation of  Hydrogen gas. Al does not react with dil H2SO4 how ever it is oxidized by hot conc. H2SO4 to displace the H2
                 2Al+6H2SO4----------> Al2(SO4)3 + 6H2O + 3SO2
Aluminium dissolves in NaOH to sodium aluminate to Hydrogen has
                 2Al+2NaOH+6H2O--------> 2NaAl(OH)4 + 3H2

Q6 Boron differ from its family members. Discuss.

        Boron is the only element of the IIIA group which is non metallic in nature.
        It is the only element with less then four electrons in vllance shell which is non-metallic.
        Boron uses its all the four electrons in bond formation so its oxidatio state is either +3 or -3.
         It gives moleculer addition compounds.
         Boron does not form ionic compounds with sulphate , nitrare as it does not from stable cation.

Q7 Write for any uses of  Aluminium ?

    Because tensile strenght it is used in making the air crafts ships and cars.
    Being non toxic in nature it is used for making food and brewing equipment and in packing.
    Being nonmegnatic it is used in navigational intruments.
    Aluminium foils are used to jam radar.

Q8 Define inert pair effect.

Ans: The ability of s electron of valance shell of lower members of IV A group to remain inert ( not involved) in bonding is called iner pair effect.

Q9 Aluminium not found in free  nature, Comment the statement.

Ans: Due to larger atomic and lower ionization energy, Al readily it valance electron and form the compound that is it not found in free state.

Q8 Ouline the four uses of broax and H3BO3

Ans: a) its used to prepair the boraz glass which is heat resistant.
        b) It is used in softing of water.
        c) It is used in metalurgical operation

Uses of Orthoboric acid

     a) It is used in pottery as a glaze
      b) Its is also used in candle indusry for stiffening of wicks
      c) Boric acid is used in medicines as antiseptic

Q9 Give  the names and composition of different boric acids.

              Ortho acid H3BO3
                MetaBoric acid HBO3
                    Tetraboric acid H2B4O7
                Pyroboric acid H6B4O9

Q10  State the procedure by which stonware are made less porus.

Ans  Stoneware usually glazed to give it a less porous surface by throwing salt upon the articles while they are hot. This treatment produces sodium aluminate and sodium aluminium silicate which melt readily and cover the entire surface. When the articles cools, the covering solidfies, producing compact smooth water proof surface.

Q11 All sheets are said to be corrosion free. Comment.

When a piece of Aluminium sheet is exposed to moist air it aquire a thin continous coating of Aluminium oxide which prevents further attack on the metal by atmospheric oxygen and water under normal conditions. Because of this Aluminium sheets are said to be corrosion free.

Q12 Borax serves as water sotening agent.

Ans: The hardness of water is due to presences of Carbonates and Biccabonates of Ca and Mg. When borax is added to haard water, it replaces the Ca+2 and Mg+2 ions by Na+1 ions. The resulting Mg borate and Ca Borate settle fown and water become soft.

Q13 H3BO3 is monobasic acid..?

Ans: Ortho boric acid is a weak acid and ionizes to very  small extent mainly monobasic acid show by the equation
                        H3BO3+H2O---------> [B(OH)4]-1 +H+

Q14  What is the formula unit Silicon Dioxide ?

Ans: The formula unit of silcon dioxide is SiO2.

Q15 What are Silicones? Give two use.

Ans: Silicones of O-Si-O chain in which the remaining bonding position of each silicon are occupied by organic groups like methyl or ethyl. The methyl silicons can be prepared. Depending upon the lenght of the cahins and degree of cross linkages between chains silicones may be liqued or rubber like materials. They are used as lubricants, Gasket and for waater proofing of fabrics.

Q16 hat are semi conductors ? Give examlps. Give two uses.

Ans: These are subtances have different resistances to the passage of current and compound like lead conditions
                  Semi conductors include elements like Germinium, Selenium and siliconand compounds like lead suphide,silicon carbide, cadium carbide, lead telluride gallium arsenide and andium antimonide.
 They are used in photo electric cells and solar batteries
They are used in the radio television, computer and calculator.

Q17 CO2 is gas while SiO2 is solid .

Ans: CO2 is exits tiny individual molecule as being smaller in size it accommodate only two oxygen atom hence found in the gaseous state whereas Silicon being larger in size can accommodate four oxygen atoms simultaneously forming the three dimensional network and hence found in solid state